At present, Multi-Input Multi-Output (MIMO) has been introduced to a Long Term Evolution-Advanced (LTE-A) system and employs a plurality of antennas at both a transmitter and a receiver for transmission and reception to thereby greatly improve the transmission performance and capacity of the system. MIMO transmission can be enabled in two schemes in uplink transmission: Single-User MIMO (SU-MIMO) and Multi-User MIMO (MU-MIMO), where SU-MIMO utilizes spatial multiplexing to transmit a plurality of data streams of a certain user over the same time and frequency resources, and MU-MIMO utilizes orthogonality between users to transmit data of the users over the same time and frequency resources. The use of MIMO enables doubling of the capacity and the spectrum efficiency of a communication system without any increase in bandwidth.
In SU-MIMO transmission of the prior art, the same time and frequency resources are occupied for a plurality of data streams, and data of each stream can be detected respectively only if an uplink channel corresponding to the each data stream (one data stream corresponds to one uplink port) is obtained by a Demodulation Reference Signal (DMRS); and the same time and frequency resources are occupied for DMRSs of different ports, and the capability of a receiver to estimate a channel of each port respectively is ensured by orthogonality of DMRS sequences. In uplink MU-MIMO transmission, the same resource is occupied for DMRSs of a plurality of users, and also the capability of a receiver to detect a respective channel of each user is ensured by orthogonality of DMRS sequences.
In order to ensure the performance of a system during SU-MIMO transmission or MU-MIMO transmission and reduce inter-layer signal interference or inter-user signal interference, an Orthogonal Cover Code (OCC) can be introduced to ensure orthogonality of DMRS sequences of different layers or different users. Especially with unequal bandwidths of multiplexed users of MU-MIMO, one user can not be distinguished from another by orthogonality of base sequences, and orthogonality can be ensured only with introduction of an OCC. However, an OCC can be suitable only for a non-slot hopping system but can not be useful for a cell with group hopping or sequence hopping. In order to enable an OCC to be used for a user with a demand in a cell, slot hopping of the corresponding user has to be disabled.
For SU-MIMO transmission or MU-MIMO transmission, it will be very difficult to ensure orthogonality between DRMS sequences if there are a large number of transmitted data streams while there is a narrow uplink transmission bandwidth and the DMRS sequences are very short. Especially in MU-MIMO transmission, orthogonality between DMRS sequences can not be ensured if there are different transmission bandwidths of multiplexed users and also their DMRS sequences are different in length. Then an OCC sequence can be introduced and two DMRS sequences of different ports are multiplied by different OCC weights to thereby ensure orthogonality between the DMRS sequences of the different ports. Referring to FIG. 1, a User Equipment (UE) does not know its own transmission mode in use, so a base station has to signal an OCC configuration to the UE. In an SU-MIMO multi-layer transmission mode, one part of DMRS ports of a user are weighted by an OCC of [1 1] (that is, free of OCC weighting), and the other part of the DMRS ports are weighted by an OCC of [1 −1], so that orthogonality of the two parts of the ports can be kept by the OCCs. If this user performs MU-MIMO transmission with another user, respective DMRS ports of the two users can be weighted respectively by [1 1] and [1 −1], so that orthogonality of DMRS sequences between the users can be ensured by the OCCs. This method can also be adopted even if the two users are configured with different bandwidths.
However, in the existing standard, whether to use group hopping or sequence hopping is configured at a cell level, and the use of either of them may result in different base sequences of two slots among DMRS sequences, thus preventing an OCC configuration from being used. In order to enable an OCC configuration be used for a user in need of an OCC function in a cell, hopping configuration has to be notified in the downlink along with a DMRS configuration (including a CS configuration and an OCC configuration) to indicate that a part of users are allowed to be configured separately with a hopping scheme different from a serving cell instead of a slot-level hopping configuration.
In the prior art, a method for indicating a CS configuration, an OCC configuration and a hopping configuration concurrently is to bind a CS configuration, an OCC configuration and a hopping configuration with a Rank Indicator (RI) and to define 8 DMRS configurations (including CS configurations, OCC configurations and hopping configurations) for each possible RI (RI=1, 2, 3 and 4). In other words, referring to FIG. 2, a user may transmit each DMRS sequence via a vary number of ports, and the total number of DMRS ports available to a single user is 4 in the existing LTE-A system, so it is required to set corresponding DMRS configurations respectively for the user using one port (i.e., Rank=1), two ports (i.e., Rank=2), three ports (i.e., Rank=3) and four ports (i.e., Rank=4); but the foregoing setting method is too complex in that corresponding DMRS configurations are set for each Rank so that the user has to reload and fetch corresponding DMRS configurations once the Rank in use is changed, thus greatly complicating the execution and increasing an operation load and also lowering the flexibility of a DMRS configuration.